Tubed tires - Why oh why do they leak?

The reason new cars use nitrogen in tires is to maintain more consistent tire pressures through temp changes, because tires get hot as you drive. I don’t have that problem in my airplanes.

What do airliners use? They go from sea level to 35,000’ and back with regularity. That’s a different problem to manage.
Jets don’t use tubes
 
The reason cars drive around with green dustcaps and 'nitrogen' in the tires is because dealerships think all car buyers are gullible. It's main purpose is to snare the car buyer to return to your service department giving you opportunity to up-sell him on other highly profitable hokum. One advantage of nitrogen is that it is completely dry, but different from a jet that goes through freeze cycles every day, that probably makes no difference.

Many years ago, Continental Tires marketed a stuff called 'Contigas' to fill tires. It was some kind of non-polar big molecule that had a substantially reduced diffusion coefficient for artificial rubber. I don't remember whether they pulled it due to lack of market acceptance or because it drilled a hole in the ozone layer. At some point the machines disappeared from the tire service places.
 
What do airliners use? They go from sea level to 35,000’ and back with regularity. That’s a different problem to manage.
I was told by an airline mechanics that nitrogen reduced the intensity of a tire fire. No oxygen to help it initially accelerate.
 
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--- done properly first bead of tire on rim ... then carefully push tube in , center stem in hole .... gently inflate a bit ... make sure valve stem remains centered .... deflate and repeat ..... this normalizes the tube fit in the tire ..... then install final tire bead .... again gently inflate and deflate to make sure tube is normalized in the space .... then high pressure to pop bead of tire securely to rim .... deflate and inflate again to proper operating pressure and make sure valve stem remains centered in hole. Use a valve stem cap with a sealing gasket in it.
Except that aircraft wheel are split. We don't force the tire over the bead. The tube is stuffed into the tire (with talc) and inflated just enough to get it to fill the tire without expanding it. Too much air and you'll be fighting to get the halves together and the bolts in. Too little air and you might get a bit of tube pinched between the halves. That ruins a tube instantly.

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Liken it to a balloon that deflates over time… it just works it’s way through a latex ballon and a non tuned tire is more like a Mylar balloon it’s less penetrative than latex
 
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